[TL-WDR3600] Upgrading from 15.05 to 19.07

Hi, I've a tplink wdr3600 with openwrt, happily using since 2015. I want to install adblock on it, but it seems possibile only in the last version on openwrt. Since it works so well, I'm kinda stuck with 15.05, my configuration works good and I don't want to mess with it and lose time to make it works so good again. I've several packages installed in extroot, and I've heard that after the upgrade I have to install everything from scratch... is there any way to upgrade from a such old version to the latest one without making any configuration? thank you

Wishfull thinking :- )

Of course, no. You want too much.